1. Field of the Invention
The present invention relates to a system for aiding optimization of a die assembly shape for plasticity manufacturing, particularly, relates to the system for aiding optimization of the die assembly shape to calculate a die assembly shape for manufacturing a plastic workpiece. Moreover, the present invention relates to a method for aiding optimization of the die assembly shape, a computer program product for aiding optimization of the die assembly shape, and a storage medium storing the computer program product.
2. Brief Description of Related Art
Conventionally, in automobile-related manufacturing industries, for example, developing a body with a light weight and high rigidity is desired. For this purpose, it is necessary to widely use a high tensile strength steel sheet. Moreover, applying an aluminium sheet is increasingly needed. However, the following problem arises: a fault in dimensional accuracy, exemplified by a springback occurring after press working a plastic workpiece. Here, the springback is defined as that a press worked metal member recovers an original shape. Therefore, for example, the shape of the workpiece which press worked in accordance with the designed shape deforms after removed from a die assembly (die and punch). FIG. 12 shows an example of the fault in dimensional accuracy caused by springback in various automobile components.
Here, a specific example of an occurrence of springback will be described with reference to FIG. 13. FIG. 13A to FIG. 13D are figures showing processes of press working for the plastic workpiece. First, a blank member 101 is installed in the die assembly (FIG. 13A.). Next, the blank member 101 is held by the die assembly with a draw bead 103 formed in the blank holder 102 (FIG. 13B.) Then, draw shaping of the blank member 101 is performed by press working which uses a die assembly 104 and a punch 105 (FIG. 13C.) Following this step, the plastic workpiece is finished by removal from the die assembly (FIG. 13D). Where, the workpiece has not been plastically shaped corresponding to the die assembly completely, but is deformed in different shape from the die assembly shape cause of the springback., i.e., the workpiece is deformed to different shape from designed shape, thus the fault of dimensional accuracy is occurred.
Therefore, conventionally, occurrence of the fault of dimensional accuracy caused by the above described springback was generally subjected to a measure by an experience and guesswork of an expert technician. The example thereof will be described with reference to FIG. 14 and FIG. 15. FIG. 14 is a flow chart showing the steps for optimization of the die assembly shape conventionally. FIG. 15 is a sectional diagrammatic figure showing the plastic workpiece.
First, according to the designed shape of the plastic workpiece (B0 of FIG. 15), namely, the designed shape supplied to step of manufacturing the product, the die assembly shape is designed (step S101.) Then, the shape of the plastic workpiece manufactured by using this die assembly is calculated by simulation (step S102.) In this step, various manufacturing conditions such as characteristics of a material of the workpiece and a press working condition are considered. Particularly, a springback characteristic of the workpiece is considered. Thus, the shape calculated becomes, as shown in FIG. 15, the shape subjected to springback from a reference point P of the workpiece to a position indicated by an arrow C (after-springback shape (B1 of FIG. 15). Evaluation of dimensional accuracy calculated for the plastic workpiece is carried out by comparing with the shape of a product by a human (step S103 and step S104.) As a result, if NG decision is made, on the basis of the shape of the product and the result of simulation, the human analyzes fault of dimensional accuracy to express as an angle difference in a predetermined part of and the position difference in coordinate values on a 2-dimensional plane to calculate the new designed shape of the plastic workpiece (step S106.) In other words, the new designed shape is calculated considering deformation by the springback after the workpiece is removed from the die assembly (springback-considered shape (Bexpxe2x80x941 of FIG. 15). The die assembly shape is corrected according to such new designed shape of the workpiece (step S107), and new die assembly shape is calculated. On the other hand, if the shape of calculated workpiece satisfies a requirement of dimensional accuracy in the step S104, an actual die assembly is manufactured according to the shape of the workpiece (step S105.)
However, the above described approach requires a human decision for the dimensional accuracy for every calculation of the shape of the plastic workpiece. In addition, for a correction of die assembly shape, it is required a much cost of die assembly correction including labor cost and cost for repeating the simulation (about 8% of the cost of die assembly manufacture) and many steps for it. As the result, the following problems arise: rise of a cost of the product and bad influence such as an increase in a period for development on a time schedule of production preparation. Consequently, a manufacturing method capable of deciding an optimal die assembly shape considering the fault of dimensional accuracy is desired in a stage where no real die assembly can be used.
On the contrary, fault of dimensional accuracy in a certain degree is expected to be forecasted by simulation using finite element method (FEM). It is in progress that the fault of dimensional accuracy in a level of 2-dimensional plane of the component is considered for design of the die assembly. A technology and system for deciding mechanically the die assembly shape properly considering a fault of 3-dimensional accuracy on the basis of the result of simulation has not been realized.
As the system for deciding a certain variables on the basis of the result of press working simulation, Japanese Published Unexamined Patent Application No. 10-170253, Japanese Published Unexamined Patent Application No. 8-287294, Japanese Published Unexamined Patent Application No. 2000-172731, have been published. All these applications are not technology and system for deciding mechanically the die assembly shape properly considering the fault of 3-dimensional accuracy.
The present invention has an objective of solving a defect of the above described conventional example and particularly improving dimensional accuracy of the plastic workpiece and providing the system, method and computer program product, for aiding optimization of the die assembly shape in plasticity manufacturing, capable of reducing a product cost and shortening manufacturing time duration.
Therefore, the present invention is constituted as that the computer comprises: an initial die assembly shape calculating function to calculate a die assembly shape for the plastic workpiece according to a predetermined designed shape of said plastic workpiece; a workpiece shape calculating function to calculate the shape of the plastic workpiece to be manufactured with the initial die assembly shape considering a manufacturing condition of the plastic workpiece; a shape comparing function to compare the calculated shape of the plastic workpiece and the designed shape of the plastic workpiece; a workpiece-redesigning function to calculate a new designed shape of the plastic workpiece according to a result of the comparison; and a die assembly reshaping function to calculate a new die assembly shape according to the new designed shape of the plastic workpiece.
And, it is preferable that the shape comparing function calculates a predetermined comparison value by comparing the predetermined designed shape of said plastic workpiece with the shape calculated by said workpiece shape calculating function, and said workpiece redesigning function and said die assembly reshaping function work each in the case where said calculated comparison value does not fall in a predetermined tolerance range in order to calculate the new die assembly shape. In this occasion, the workpiece shape calculating function is preferably calculates the shape of the plastic workpiece considering the springback characteristic of the predetermined material used for the plastic workpiece.
According to such configuration, first, an operator inputs data of the designed shape of the plastic workpiece to the computer and the die assembly shape used for the plastic workpiece is calculated by the computer on the basis of the designed shape data. Next, the shape of the plastic workpiece manufactured with this die assembly shape by press working is simulated by the computer. In this step, the shape of the plastic workpiece calculated considers the springback characteristic of the material. Then, the calculated shape of the plastic workpiece is compared with the designed shape of the plastic workpiece for calculating the comparison value. In such case, the comparison value has a value according to the springback characteristic of the plastic workpiece.
In the case where the comparison value is kept within a predetermined tolerance, in the other word, the calculated shape of the plastic workpiece is in a range of an error allowable against the designed shape, the simulation is finished in the status and the first calculated die assembly shape is decided to be the die assembly for actually manufacturing. On the other hand, in the case where the comparison value is larger than the tolerance, the computer calculates the new designed shape of the plastic workpiece on the basis of comparison value. The die assembly shape allowing manufacture of this new designed shape is calculated by the computer.
Therefore, the new designed shape of the plastic workpiece, of which fault of dimensional accuracy caused by influence of the springback characteristic of the plastic workpiece is automatically corrected, is calculated. The new die assembly shape is calculated according to this step and therefore, the dimensional accuracy can be improved and a time consumed for optimization of the die assembly by simulation can be shortened, resulting in shortening a time for product development and reducing a cost of the product.
It is preferable that the workpiece shape calculating function also works on the new die assembly shaped by the die assembly reshapeing function. Accordingly, the new die assembly shape is calculated for correction of fault of dimensional accuracy of the plastic workpiece of which shape is once calculated by simulation. The shape of the plastic workpiece manufacturable by using this new die assembly shape is calculated by simulation. The calculated shape of the plastic workpiece is compared with the predetermined designed shape, the new designed shape of the plastic workpiece, of which fault of dimensional accuracy has been corrected, is again calculated, and the new die assembly shape based on the new designed shape of the plastic workpiece is calculated. Thus, by repeating correction of fault of dimensional accuracy, it is possible to calculate the die assembly shape automatically for manufacturing the plastic workpiece of higher dimensional accuracy by simulation only.
In addition, it is preferable that the shape comparing function calculates an amount of springback, which is a difference between the shape of the plastic workpiece calculated considering the springback characteristic and the predetermined designed shape of the plastic workpiece for each predetermined position of the plastic workpiece, and the workpiece-redesigning function calculates the new designed shape of the plastic workpiece by subtracting the springback amount from the designed shape of the plastic workpiece in an opposite direction of a springback direction of the plastic workpiece in each position of the plastic workpiece. In these step, the shape comparing function compares an angle of the plastic workpiece in a predetermined position and compares 3-dimensional positions of predetermined nodes set on the plastic workpiece.
By this, correction of the die assembly shape is performed considering a deformation amount of the plastic workpiece caused by the springback. Hence, simulation can optimize the die assembly shape quickly manufacturable of the plastic workpiece of the higher dimensional accuracy. In other words, realizing improvement of dimensional accuracy of the workpiece, a frequency of repeated calculating of the new die assembly shape can be restricted to realize shortening of die assembly producing period.
Also, the system for aiding optimization of a die assembly shape for plasticity manufacturing, wherein the computer comprises a producibility judging function to judge the presence of deficiency upon producing the plastic workpiece based on the new designed shape of the plastic workpiece calculated by the workpiece-redesigning function. Moreover, the system for aiding optimization of a die assembly shape for plasticity manufacturing, wherein the producibility judging function comprises a draft calculating function to calculate a draft of the new designed shape of the plastic workpiece calculated by the workpiece-redesigning function, and a draft comparing function to judge the producibility of the plastic workpiece by comparing the value of the calculated draft and the value of the predetermined allowable draft.
According to this approach, first, drafts at various parts of the new designed shape are calculated considering the deformation amount of the plastic workpiece caused by springback. Then, the drafts are compared to the predetermined draft value in the allowable range to judge whether or not the plastic workpiece is actually producible (producibility). Therefore, deficiency caused by correcting the designed shape can be found at the simulation stage, thus being able to deal with the problem at an early stage. As a result, further cost for correcting the die assembly can be reduced and time required for designing the die assembly can be shortened. Whether or not the plastic workpiece can be produced into the new designed shape is not necessarily judged based on the values of the drafts.
Also, the system for aiding optimization of a die assembly shape for plasticity manufacturing, wherein the computer comprises a producibility notifying function to notify the operator of the computer of the judgment result from the producibility judging function. Specifically, the system for aiding optimization of a die assembly shape for plasticity manufacturing, wherein the computer comprises a draft propriety notifying function which operates when the draft calculated by the draft comparing function is smaller than the allowable draft and notify the operator of that position.
According to this approach, any deficiency such as the plastic workpiece being unproducible is immediately notified to the operator. Therefore, the operator can take a suitable measure, for example, manually terminating the die assembly correction process, or changing the designed shape of the notified position.
Furthermore, the system for aiding optimization of a die assembly shape for plasticity manufacturing, wherein the computer comprises an optimization process terminating function to terminate execution of the process for optimizing the die assembly shape when the producibility judging function judges that the plastic workpiece is unproducible. According to this approach, the process for correcting the die assembly based on the designed shape that is potentially unproducible is automatically terminated. Accordingly, useless processes can be minimized, time for designing the die assembly can be shortened, and the cost can be reduced.
The present invention provides a method for aiding optimization of a die assembly shape to manufacture a predetermined plastic workpiece by using a computer, wherein, the method comprising the steps of: calculating an initial die assembly shape for the plastic workpiece according to a predetermined designed shape of said plastic workpiece; calculating a shape of the plastic workpiece to be manufactured with the initial die assembly shape considering a manufacturing condition of the plastic workpiece; comparing the calculated shape of the plastic workpiece with the designed shape of the plastic workpiece; calculating a new redesigned shape of the plastic workpiece on the basis of a result of the comparison; and calculating a new die assembly shape according to the redesigned shape of the plastic workpiece. Here, it is preferably, the method for aiding optimization of a die assembly shape for plasticity manufacturing according to claim 13, wherein the method further comprises, between the step of redesigning the plastic workpiece and the step of reshaping the die assembly, a step of judging the presence of deficiency upon producing the plastic workpiece based on the new designed shape of the plastic workpiece calculated in the step of redesigning the plastic workpiece.
Moreover, the present invention also provides a computer program product stored in storage medium for aiding optimization of the die assembly shape to manufacture the predetermined plastic workpiece by controlling an operation of the computer, wherein the program product performing the processes of: calculating an initial die assembly shape for the plastic workpiece according to a predetermined designed shape of said plastic workpiece; calculating a shape of the plastic workpiece to be manufactured with the initial die assembly shape considering a manufacturing condition of the plastic workpiece; comparing the calculated shape of the plastic workpiece with the designed shape of the plastic workpiece; calculating a new redesigned shape of the plastic workpiece on the basis of a result of the comparison; and calculating a new die assembly shape according to the redesigned shape of the plastic workpiece. Also, present invention provide a storage medium storing the computer program product. Above mentioned computer program product for aiding optimization of the die assembly shape for plasticity manufacturing according to claim 15, wherein the program product controls the computer to execute a process of judging the presence of deficiency upon producing the plastic workpiece based on the new designed shape of the plastic workpiece calculated in the step of redesigning the plastic workpiece.
These steps also provide influences and effects similar to those as describe above.